Quote: "Watch how the gravity value decrements the y velocity of the apples"

Very odd choice...

Walking & Jumping: The code has a "x_velocity" (a misleading variable name...) of 10, but for some reason the demo has a "speed" input box, and the left & right motion not only doesn't match that value, it's different for each direction (?)

I wouldn't call this a good tutorial...

Edit: I would recommend reading the tutorial linked at the end first, especially the terms' definitions.